Narrow band interference supressor

Abstract

A compact narrow band interference suppressor. The narrow band interference suppressor includes a plurality of interference signal elimination circuits, a frequency compensation circuit, an AGC amp, and an AD converter that are connected in series. Each interference signal elimination circuit includes a mixer for synthesizing a local oscillation signal of a variable frequency oscillator to eliminate an interference signal with a band elimination filter. The frequency compensation circuit includes a mixer for synthesizing a signal having a frequency generated by the variable frequency oscillator to restore the signal to the frequency band of the signal input to the narrow band interference suppressor by the variable frequency oscillator. The AD converter converts the polarity of the signal in accordance with the number of times the signal passes through the mixer.

1 . A narrow band interference suppressor for eliminating an interference signal from a broadband input signal, the narrow band interference suppressor comprising: 
 a plurality of interference signal elimination means, each including a narrow band signal elimination filter, each interference signal elimination means synthesizing the input signal and a local oscillation signal to eliminate an interference signal with the narrow band signal elimination filter, wherein the local oscillation signal has a frequency that is calculated and determined based on the frequency of the local oscillation signal that has been synthesized in the interference signal elimination means preceding the interference signal elimination means that is to synthesize the local oscillation signal.    
   
   
       2 . The narrow band interference suppressor according to  claim 1 , further comprising: 
 a compensation means, located at an output side of the final interference signal elimination means, for synthesizing the local oscillation signal to match the frequency band of an output signal of the narrow band interference suppressor to the frequency band of the broadband input signal, wherein the compensation means synthesizes a local oscillation signal having a frequency determined based on the frequency of the local oscillation signal synthesized in each interference signal elimination means.    
   
   
       3 . The narrow band interference suppressor according to  claim 2 , wherein each interference signal elimination means includes a variable frequency oscillation means for generating a local oscillation signal, the narrow band interference suppressor further comprising: 
 a control means for determining the frequency of the local oscillation signal of the variable frequency oscillation means, wherein the control means:    specifies the frequency of an interference signal included in the broadband input signal;    calculates the frequency of the interference signal when the frequency of the interference signal is synthesized with the local oscillation signal in the preceding interference signal elimination means and input to the variable frequency oscillation means; and    generates a frequency, obtained by adding the frequency to a frequency of a signal that can be eliminated by the narrow band signal elimination filter, in the variable frequency oscillation means of the interference signal elimination means.    
   
   
       4 . The narrow band interference suppressor according to  claim 3 , wherein the input signal includes an in-phase component and a quadrature component, the narrow band interference suppressor further comprising: 
 a detection means, located at the output side of the final interference signal elimination means, for separating the in-phase component and the quadrature component from the input signal; and    an analog-to-digital conversion means for converting an analog signal to a digital signal, wherein the analog-to-digital conversion means reverses polarity of one of the in-phase component and the quadrature component when the local oscillation signal is synthesized an odd number of times in the interference signal elimination means and the compensation means.    
   
   
       5 . The narrow band interference suppressor according to any one of  claims 1  to  4 , further comprising: 
 a delay means located at the input side of the first stage interference signal elimination means, wherein the delay means has a delay time that is longer than the time necessary for the control means to determine the frequency of the local oscillation signal synthesized in the interference signal elimination means and output the local oscillation signal having this frequency.    
   
   
       6 . The narrow band interference suppressor according to any one of  claims 1  to  5 , further comprising: 
 an automatic gain control amplifier located at the output side of the interference signal elimination means.